Procainamide is the most common cause of drug-induced lupus (DIL). Autoantibodies to histone complex (H2A-H2B)-DNA have been associated with DIL due to procainamide. We propose a longitudinal study looking for IgG and IgM antibodies to (H2A-H3B)-DNA in patients on procainamide. Sera for antibody testing will be obtained from patients every 3 months for up to 36 months and clinical evaluation for DIL will be done at the same time. We hypothesize patients who develop IgG to (H2A-H2B)-DNA will go on to develop DIL.